appveyor: cleanup unnecessary leftovers
appveyor: cleanup unnecessary leftovers

- platform is optional and matters for Visual Studio builds
- `ver` command shows the windows version
and was just my first CI test

mje-nz/PX4-Firmware,krbeverx/Firmware,dagar/Firmware,PX4/Firmware,dagar/Firmware,krbeverx/Firmware,krbeverx/Firmware,acfloria/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,dagar/Firmware,dagar/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,PX4/Firmware,PX4/Firmware,krbeverx/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,PX4/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,acfloria/Firmware,dagar/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,dagar/Firmware,krbeverx/Firmware,krbeverx/Firmware,krbeverx/Firmware,acfloria/Firmware,PX4/Firmware